CTechBlueDragon - in New Zealand, we are only allowed to run 1x spacer and using a spacer on the inside would restrict wheel options/offset if so desired. While it is not a issue when using longer studs, it is all dependent on what lengths the person who is modifying will go to install said components.
For me, I considered the available options and methods, considered my vehicle certification requirements in New Zealand and subsequently have decided that for my application, mounting the st205 calipers was not a cost effective method to get good braking. Considering that a set of st205 calipers cost approx $450NZ on the second hand market and not readily available, while a brand new pair of wilwood superlites cost $550NZ.
It really is dependent on circumstance and applicable laws around modification. If my car was strictly for motorsport, then there is more room for modification, but at the end of the day, I build to the letter of the local regulations.
Bruce - when a st205 caliper is mounted to the st165/185 hub, the allowable outer circumference of the rotor is 295mm (305mm minus 10mm). This circumference is not definitive with the rotor circumference ranging from 295mm to 300mm. UK peeps sometimes use a 294x25mm wrx rotor using a 6mm brake pad spacer to offset the rotor thickness differences between st205 and wrx rotors (can't remember if they used a spacer behind the disc).
Alternatively, some have used Altezza RS200/Supra 300mm discs redrilled to 5x100 and taken 2-3mm off the hub mounting points to change the offset of the caliper to the Altezza rotor.
And with all this work, a bell and rotor setup has been made as well as a dog bone adapter.
All to get that little Celica logo on the brakes...